The invention generally relates to piston machines. More specifically, the invention relates to piston machines of the type comprising a housing, in which at least one piston is arranged which can be moved to and fro between two end positions in order to periodically increase and reduce the size of a working chamber, wherein the piston has a guiding member which is in engagement with a control curve of a curve member arranged in the housing.
A piston machine according to the present invention can be used, in particular, as an internal combustion engine. In the present description, the use of the piston machine as an internal combustion engine is presented as the preferred use. However, there are other possible uses of a piston machine according to the present invention, e.g. use of the piston machine as a compressor.
WO 2006/122658 A1 discloses a piston machine which is of the type of a rotary piston machine. A total of four pistons is arranged in the housing of the known piston machine, and these pistons run jointly around an axis of revolution which is fixed relative to the housing. As they run jointly around the axis of revolution, the four pistons perform reciprocating movements, two pistons in each case, which form a piston pair, performing reciprocating movements in opposition to one another in order alternately to increase and reduce the size of a working chamber defined between the end faces of the two pistons of the piston pair. Overall, the known rotary piston machine has two working chambers, and the working chambers increase and decrease in size in the same sense. The four pistons are mounted in a sliding manner in a piston cage which revolves around the axis of revolution together with the pistons.
If the known rotary piston machine is used as an internal combustion engine, the operating strokes of induction, compression, expansion and exhaust take place during the periodic decrease and increase in the size of the volumes of the working chambers.
In this arrangement, the reciprocating movements of the individual pistons are derived from the revolution of the pistons about the axis of revolution since the pistons each have a guiding member which runs in a control curve of a curve member fixed relative to the housing, the control curve having a corresponding undulating contour to enable the reciprocating movements of the pistons to be derived from the revolution of the pistons about the axis of revolution.
If such a rotary piston machine is used as an internal combustion engine, the revolution of the piston cage can be transmitted to an output shaft in order to drive a vehicle, for example.
Further rotary piston machines of a comparable type are known from DE 10 2005 024 751 A1 or from WO 03/067033 A1, for example. In the rotary piston machine known from DE 10 2005 024 751 A1, the curve member is integrated directly into the inner wall of the housing, as is the case also with the rotary piston machine known from WO 03/067033 A1.
With the known piston machines described above, a disadvantage results from the fact that the reciprocating movements of the pistons which define the operating strokes of induction, compression, expansion and exhaust are derived from a revolution of the pistons about the axis of revolution and that the piston cage also necessarily revolves about the axis of revolution together with the pistons. Owing to the revolution of the pistons about the axis of revolution, they are acted upon by centrifugal forces, which lead to friction phenomena, caused by centrifugal forces, between the outer walls of the pistons and the inner wall of the piston rotor since, although the pistons revolve jointly with the piston cage, they have to perform reciprocating sliding movements relative to the piston cage. Owing to the centrifugal forces acting on the pistons, these reciprocating movements are thus subject to friction. The centrifugal forces acting on the pistons therefore impair the running characteristics of the known piston machines.
DE 101 15 167 C1 has furthermore disclosed a high-pressure radial-piston pump, in particular as a fuel pump for injection systems of internal combustion engines. In a pump head, this high-pressure pump has radially movable pump pistons, the reciprocating movements of which are generated by a rotatable cam ring which surrounds the pump pistons and has a correspondingly contoured cam track.